A hybrid vehicle comprises an internal combustion thermal engine, which transmits torque to the driving wheels by means of a transmission provided with a gearbox, and at least one electric machine which is electrically connected to an electric storage system and mechanically connected to the driving wheels.
The electric power system of a hybrid vehicle comprises a storage device provided with a chemical battery pack and a two-way electronic DC/AC power converter, which is connected to the storage device on the DC side and is connected to the electric machine on the AC side, and has the function of controlling the electric machine itself.
The chemical batteries used in current road vehicles with hybrid propulsion may have high specific storable electric energy (i.e. per unit of mass and/or volume) and low specific deliverable electric power (i.e. per unit of mass and/or volume), and thus be adapted to meet the needs of a long trip traveled at constant speed (and, especially, with limited accelerations/decelerations). Alternatively, the chemical batteries used in current road vehicles with hybrid propulsion may have low specific storable electric energy (i.e. per unit of mass and/or volume) and high specific deliverable electric power (i.e. per unit of mass and/or volume), and thus be adapted to meet the needs of a short trip traveled at high speed (and, especially, with fast accelerations/decelerations).
In order to attempt to obtain an acceptable trade-off between range needs (for which chemical batteries which have high specific electric energy are required) and performance needs (for which chemical batteries which have high specific electric power are required), it has been attempted to manufacture trade-off chemical batteries which have intermediate features between the two extremes; however, it has been observed that such trade-off chemical batteries are a “second-rate” trade-off, i.e. the significant reduction of specific electric energy does not correspond to an equally significant increase of specific electric power, and vice versa.
In order to attempt to obtain an acceptable trade-off between range needs (for which chemical batteries which have high specific electric energy are required) and performance needs (for which chemical batteries which have high specific power are required), it has also been suggested to include both chemical batteries which have high specific electric energy and chemical batteries which have high specific energy in the storage system. However, the overall results (in terms of range and performance) and in particular the operative lifespan of the chemical batteries have been found not to be entirely satisfactory because the “final result” was in some way inferior to the sum of the single parts.
Italian patent application BO2012A000315 describes an electric power system of a vehicle with electric propulsion; the electric power system has: a pair of connected electric machines; a storage system comprising two chemical battery packs electrically separated from each other; a pair of electronic DC/AC power converters, each of which exchanges electric energy with the storage system and controls a corresponding electric machine; and a pair of electronic DC/DC power converters, each of which increases the voltage and has a low-voltage side, which is electrically connected only and exclusively to a corresponding chemical battery pack, and a high-voltage side, which is connected to both electronic DC/AC power converters in parallel to the high-voltage side of the other electronic DC/DC power converter. However, the electric power system described in Italian patent application BO2012A000315 has relatively high dimensions.
Patent application EP2117106A1 describes an electric power system of a vehicle with electric propulsion; the electric power system comprises:
two electric machines MG1 and MG2;
a storage system comprising two chemical battery packs 10 and 20 electrically separated from each other;
a first electronic DC/AC power converter INV1, which exchanges electric energy with the storage system and controls a first electric machine MG1;
a second electronic DC/AC power converter INV2, which exchanges electric energy with the storage system and controls a second electric machine MG2;
a first electronic DC/DC power converter 18, which increases the voltage and has a low-voltage side, which is electrically connected only and exclusively to a first chemical battery pack 10, and a high-voltage side, which is connected to both electronic DC/AC power converters INV1, INV2; and
a second electronic DC/DC power converter 28, which increases the voltage and has a low-voltage side, which is electrically connected only and exclusively to a second chemical battery pack 20, and a high-voltage side, which is connected to both electronic DC/AC power converters INV1, INV2 in parallel to the high-voltage side of the first electronic DC/DC power converter CONV1.